Electrochemical and antioxidant properties of rutin

Article abstract of DOI:10.1135/cccc2009548

The mechanism of electrochemical oxidation of rutin on a glassy carbon electrode was studied at different pH by using several electrochemical techniques (cyclic, linear sweep, differential pulse and square-wave voltammetry) in order to give deeper insight into the mechanism of electrochemical oxidation of rutin and adsorption of its oxidation products on a glassy carbon electrode. It was determined that the rutin oxidation process on a glassy carbon electrode is reversible, pH dependent and includes the transfer of 2 e^- and 2 H⁺. The products of electrochemical oxidation strongly adsorb on the electrode surface. Maximum surface coverage, _max, decreased with increasing scan rate from 3.4 × 10^-9 mol cm^-2 at scan rate 20 mV s^-1 to 1.5 × 10^-9 mol cm^-2 at scan rate 100 mV s^-1 and adsorption equilibrium constant was log K = 4.57 ± 0.05. Antioxidant properties of rutin were investigated by a Trolox equivalent antioxidant capacity (TEAC) assay. It was found that the TEAC values of rutin depend on concentration and the EC₅₀ value of rutin amounted 0.23.

Full text of DOI:10.1135/cccc2009548

Electrochemical and Antioxidant Properties of Rutin
547
ELECTROCHEMICAL AND ANTIOXIDANT PROPERTIES OF RUTIN
a,
b2
Martina MEDVIDOVIĆ-KOSANOVIĆ *, Marijan ŠERUGAb1, Lidija JAKOBEK and
b3
Ivana NOVAK
a
Department of Chemistry, J. J. Strossmayer University, F. Kuhača 20, HR-31000 Osijek, Croatia;
e-mail: mmkosano@kemija.unios.hr
b Faculty of Food Technology, J. J. Strossmayer University, F. Kuhača 18, HR-31000 Osijek, Croatia;
1
2
3
e-mail: marijan.seruga@ptfos.hr, lidija.jakobek@ptfos.hr, ivana.novak@ptfos.hr
Received November 10, 2009
Accepted January 21, 2010
Published online May 17, 2010
The mechanism of electrochemical oxidation of rutin on a glassy carbon electrode was stud-
ied at different pH by using several electrochemical techniques (cyclic, linear sweep, dif-
ferential pulse and square-wave voltammetry) in order to give deeper insight into the
mechanism of electrochemical oxidation of rutin and adsorption of its oxidation products
on a glassy carbon electrode. It was determined that the rutin oxidation process on a glassy
carbon electrode is reversible, pH dependent and includes the transfer of 2 e– and 2 H+. The
products of electrochemical oxidation strongly adsorb on the electrode surface. Maximum
surface coverage, Γmax, decreased with increasing scan rate from 3.4 × 10–9 mol cm–2 at scan
rate 20 mV s–1 to 1.5 × 10–9 mol cm–2 at scan rate 100 mV s–1 and adsorption equilibrium
constant was log K = 4.57
0.05. Antioxidant properties of rutin were investigated by a
Trolox equivalent antioxidant capacity (TEAC) assay. It was found that the TEAC values of
rutin depend on concentration and the EC50 value of rutin amounted 0.23.
Keywords: Polyphenols; Antioxidants; Rutin; Electrochemistry; Oxidation; Adsorption; Anti-
oxidant properties; TEAC assay; Differential pulse; Square-wave voltammetry.
Phenolic compounds or polyphenols are naturally occurring group of com-
ponds which are responsible for brightly coloured pigments present in a va-
riety of fruits and vegetables and protect plants from diseases and
ultraviolet light. They are products of the secondary metabolism of plants
and arise from two main primary synthetic pathways: the shikimate path-
way and the acetate pathway. Depending on their basic structure,
polyphenols can be divided into at least 10 different classes. Flavonoids
constitute one of the most important groups and their common structure
consists of two aromatic rings linked through three carbons that usually
form an oxygenated heterocycle (C6-C3-C6). Based on structural differences,
flavonoids can be subdivided into several families: flavonols (e.g. quercetin,
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© 2010 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc2009548

548
Medvidović-Kosanović, Šeruga, Jakobek, Novak:
rutin and kaempferol), flavones (e.g. luteolin, apigenin and chrysin),
flavanols (e.g. catechin and related compounds) isoflavones (e.g. genistein),
flavanones (e.g. hesperidin, naringenin), flavanonones (e.g. astilbine,
engeletine),
cis-flavan), chalkones (e.g. buteine, mareine, floretine), dihydrochalkones
(e.g. crotaramine, crotine, acumitine), flavane-3,4-diols (e.g.
flavanes
(e.g.
3,4-trans-3′,4′-dimethoxy-6-methyl-2,3-
leukopelargonidine, leukocyanidine) and anthocyanidins (e.g. cyanidin,
delphinidin, malvidin, etc. and their related glycosides)1. Most of the bene-
ficial health effects of flavonoids (anti-inflammatory, anti-cancer, cardio
protective) are attributed to their antioxidant and chelating abilities2,3
.
Since the chemical activities of flavonoids in terms of their reducing prop-
erties as hydrogen or electron-donating agents could predict their potential
to act as antioxidants (lower oxidation potential points to higher antioxi-
dant activity)4, studying of electrochemical and antioxidant properties
could help in better understanding of the mentioned group of compounds.
In the last two decades flavonoids were studied by different techniques.
Electrochemical properties of flavonoids were studied by voltammetric
techniques (cyclic voltammetry5–16,20
,
differential pulse voltam-
metry5,7,10,15,17,18,21, square-wave voltammetry5,16,19, linear sweep voltam-
metry7, chronocoulometry6) and UV spectroelectrochemistry12. Anti-
oxidant capacity of flavonoids was studied by cyclic voltammetry19,22–25
,
,
differential pulse voltammetry26
,
flow injection analysis (FIA)27,28
chronoamperometry29, biosensors21,30, UV/Vis spectroscopy (with different
reagents e.g. Folin–Ciocalteau19,30, FRAP 22, DPPH 19,29, ABTS 19,30, etc.),
photochemiluminescence19, spectrofluorimetry (ORAC method)30 and elec-
tron spin resonance (ESR) spectroscopy31. Possible oxidation mechanisms
of rutin and its detection limits are given in Table I.
The flavonoid rutin (quercetin-3-O-rutinose), also known as vitamin P, is
one of the most bioactive flavonoids usually found in plants (especially
buckwheat), black tea and apple peels. In humans, it attaches to the iron
ion (Fe2+), preventing it from binding to hydrogen peroxide and creating
a highly reactive free radical that may damage cells. Rutin may have anti-
oxidant, anti-inflammatory, anti-tumor, anti-thrombotic, cardio protective
and antibacterial activity32. It increases the strength of the walls of blood
capillaries and regulates their permeability. Therefore, rutin can reduce the
symptoms of many other capillary diseases. The chemical structure of rutin
is given in Fig. 1.
The purpose of this study was to apply electrochemical methods (cyclic,
differential pulse and square-wave voltammetry) in systematic investigation
of electrochemical properties of rutin and to study rutin adsorption on the
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Electrochemical and Antioxidant Properties of Rutin
549
TABLE I
Possible oxidation mechanisms of rutin and its limits of detection (LOD)
LOD,
Method
Possible oxidation mechanism
Ref.
mol dm–3
Cyclic voltammetry, differential n.a.a
pulse voltammetry, square-wave
voltammetry
2 e–, 2 H+ reversible oxidation
(3′,4-dihydroxy group) followed by
irreversible oxidation
5
(5,7-dihydroxy group)
Cyclic voltammetry
1 × 10–8
2 e–, 2 H+ reversible oxidation
6
(3′,4-dihydroxy group)
Differential pulse voltammetry
Cyclic voltammetry
2.51 × 10–8
n.a.a
2 e–, 2 H+ reversible oxidation
(3′,4-dihydroxy group)
7
quasi-reversible electrochemical
process involving 2 e–
8
Cyclic voltammetry
n.a.a
2 e–, 2 H+ reversible oxidation
9
(3′,4-dihydroxy group)
Differential pulse voltammetry
1 × 10–8
quasi-reversible electrochemical
process involving 2 e–
10
Linear sweep voltammetry
Cyclic voltammetry
1.5 × 10–7
n.a.a
irreversible process
13
15
oxidation (3′,4-dihydroxy group)
followed by irreversible oxidation
(5,7-dihydroxy group)
Square-wave voltammetry
1 × 10–8
1 × 10–8
4 × 10–8
n.a.
n.a.
16
17
Differential pulse voltammetry
Differential pulse voltammetry
2 e–, 2 H+ oxidation (3′,4-dihydroxy 18
group) followed by irreversible
oxidation (5,7-dihydroxy group)
Square-wave voltammetry
Cyclic voltammetry
1 × 10–9
3.58 × 10–7
n.a.
19
20
2 e–, 2 H+ reversible oxidation
(3′,4-dihydroxy group)
Square-wave voltammetry
1.75 × 10–7
n.a.
21
Cyclic voltammetry, rotating
ring-disk voltammetry
n.a.a
2 e–, 2 H+ quasi-reversible oxidation 34
(3′,4-dihydroxy group) followed by
irreversible oxidation (5,7-dihydroxy
group)
a
n.a. = not available.
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Medvidović-Kosanović, Šeruga, Jakobek, Novak:
glassy carbon electrode (by linear sweep voltammetry), in order to give
deeper insight into the mechanism of electrochemical oxidation of rutin
and adsorption of its oxidation products on a glassy carbon electrode. Anti-
oxidant capacity and EC50 value of rutin were determined by a Trolox
equivalent antioxidant capacity (TEAC) assay. The obtained results can be
used to explain the connection between electrochemical properties of rutin
and its biological activity.
FIG. 1
Chemical structure of rutin (3′,4′,5,7-tetrahydroxyflavone-3β-D-rutinoside)
EXPERIMENTAL
All chemicals were of the highest purity commercially available and were used without further
purification. Rutin trihydrate (C27H30O16·3H2O) and 2,2′-azinobis(3-ethylbenzothiazoline-
6-sulfonic acid) diammonium salt (ABTS) were obtained from Sigma (St. Louis, MO, USA).
( )-6-Hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) was purchased from
Fluka (Buchs, Switzerland). All other chemicals were obtained from Kemika (Zagreb,
Croatia). Stock solution of rutin c = 1 × 10–2 mol dm–3) was prepared in methanol and kept
in the refrigerator (solution was stable for at least 1 month). Prior to use, stock solution was
diluted to the desired concentration with buffer supporting electrolyte (Ic = 0.1 mol dm–3).
Buffer supporting electrolyte solutions were prepared in high-purity water from a Millipore
Milli-Q system (resistivity greater than or equal to 18 MΩ cm). A phosphate buffer solution
of pH 8.0 and 7.0, an acetate buffer solution of pH 5.5, 4.5 and 3.5, and a hydrochloride
buffer solution of pH 2.5 were used.
The electrochemical experiments were preformed with an EG&G Princeton Applied
Research Model 273A potentiostat controlled by a computer in a three-electrode system,
consisting of a glassy carbon working electrode (Bioanalytical System, d = 3 mm), a saturated
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Electrochemical and Antioxidant Properties of Rutin
551
calomel reference electrode (SCE) and a platinum counter electrode. The glassy carbon work-
ing electrode was polished with α-Al2O3 powder (0.05 µm, Buehler, USA) before each mea-
surement. Linear sweep voltammograms were performed at 20, 50 and 100 mV s–1. Cyclic
voltammetry scan rate was 50 mV s–1. The differential pulse voltammetry conditions were:
scan increment 5 mV, pulse amplitude 50 mV, pulse width 70 ms and scan rate 5 mV s–1
.
Square-wave voltammetry conditions used were: frequency 50 Hz, pulse amplitude 50 mV
and scan increment 2 mV (effective scan rate 100 mV s–1).
Antioxidant properties of rutin were investigated by a TEAC decolourisation assay on a
J. P. Selecta UV/Vis spectrophotometer Model UV 2005. A stock solution of ABTS radical cat-
ion was prepared by mixing 0.2 ml ammonium peroxodisulfate solution (c = 65 mmol dm–3
)
with 50 ml of ABTS solution (c = 1 mmol dm–3) in phosphate buffer (Ic = 0.1 mol dm–3
NaH2PO4, pH 7.40). The mixture was left to stand overnight. A 0.5 ml of ABTS radical cation
stock solution was put into the 1 cm glass cuvette, diluted with 2 ml of phosphate buffer
and the absorbance of the ABTS radical cation at 734 nm was read. Subsequently, 0.1 ml
of sample solution was added into the cuvette, the solution was quickly mixed and
the absorbance was monitored at 734 nm for 60 s. The decrease of absorbance after 60 s
(∆Asample) was compared with the decrease of absorbance caused by the addition of 0.1 ml of
Trolox solution (c = 400 µmol dm–3) (∆ATrolox) and the TEAC value was calculated according
to the formula27
–1
TEAC = ∆Asample cTrolox (∆ATrolox csample
)
.
(1)
The pH measurements were carried out at room temperature with a Metrel MA 5736
pH-meter.
RESULTS AND DISCUSSION
Cyclic Voltammetry
In order to obtain general information regarding electrochemical properties
and possible surface activity of rutin the cyclic voltammetry measurements
were performed. Cyclic voltammograms of rutin (c = 1 × 10–5 mol dm–3)
were recorded in buffer solutions (Ic = 0.1 mol dm–3) in pH range 2.5–8.0.
An example of cyclic voltammogram of rutin recorded at pH 4.5 from 0 to
0.6 V is shown in Fig. 2B. It can be seen that there is one reversible oxida-
tion peak at the potential, Ep,a = 0.401 V, which corresponds to the oxida-
tion of the 3′,4′-dihydroxy substituent on the B-ring of rutin. The reduction
peak of the 3′,4′-diquinone formed during rutin oxidation process, ap-
peared at Ep,c = 0.364 V. The peak separation is ∆Ep = Ep,a – Ep,c = 37 mV,
which points to reversible electrode reaction involving two electrons on the
glassy carbon electrode5,7–9. The reversibility of the rutin oxidation process
can be seen from Fig. 2C as well, since the decrease of anodic potential
limit has shown that the reduction peak appears even if the anodic poten-
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Medvidović-Kosanović, Šeruga, Jakobek, Novak:
tial is inverted immediately after the oxidation peak of rutin. It can also be
seen from the Fig. 3A since linear dependence was found between anodic
peak current and the square root of scan rate, which also shows that the
rutin oxidation is controlled by diffusion11. Adsorption process on the elec-
trode surface was confirmed by increase of reduction peak current with in-
creasing scan rate, Ip,c(v)–1/2 vs log v plot (Fig. 3B)33. Even dough, there can
be found a second oxidation peak of rutin above 0.6 V in the relevant liter-
ature5,9, extension of measurements to 1.2 V has not revealed a second oxi-
dation peak of rutin in our cyclic voltammetry measurements (Fig. 2A).
B
A
E, V vs SCE
E, V vs SCE
C
E, V vs SCE
FIG. 2
Cyclic voltammograms of rutin (c = 1 × 10–5 mol dm–3) in acetate buffer (Ic = 0.1 mol dm–3, pH
5.5 (A); pH 4.5 (B)) at scan rate 50 mV s–1. (C) Cyclic voltammogram of rutin (c = 1 × 10–5
mol dm–3) in acetate buffer (Ic = 0.1 mol dm–3, pH 4.5) at scan rate 50 mV s–1. First scan (be-
tween 0 and 0.60 V) (a), second scan (between 0 and 0.55 V) (b), third scan (between 0 and
0.50 V) (c), forth scan (between 0 and 0.45 V) (d)
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Electrochemical and Antioxidant Properties of Rutin
553
Linear Sweep Voltammetry
According to data found in literature, the products of electrochemical oxi-
dation of rutin strongly adsorb on the glassy carbon electrode surface5. In
order to study this phenomena linear sweep voltammetry was used. The re-
lationship between peak current (Ip) and rutin concentration (from 8 × 10–6
to 1 × 10–4 mol dm–3) in acetate buffer (Ic = 0.1 mol dm–3, pH 4.5) was stud-
ied at scan rates 20, 50 and 100 mV s–1. The results have shown that anodic
peak current increased proportionally with scan rate and rutin concentra-
tion. Linear sweep voltammetry data obtained at different scan rates were
A
1/2
1/2 –1/2
, mV s
v
B
–1
log v, mV s
FIG. 3
(A) Anodic peak current of rutin solutions (Ic = 0.1 mol dm–3, pH 4.5) as a function of the
square root of scan rate. c(rutin) = 1 (᭹), 10 (᭿), 70 (ꢀ), 200 (᭜) µmol dm–3. (B) Dependence of
Ip(v)–1/2 for cathodic peak current of rutin solutions (Ic = 0.1 mol dm–3, pH 4.5) as a function of
the logarithm of scan rate. c(rutin) = 1 (᭹), 10 (᭿), 70 (ꢀ), 200 (᭜) µmol dm–3
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554
Medvidović-Kosanović, Šeruga, Jakobek, Novak:
used to calculate surface coverage (Γ) of the glassy carbon electrode accord-
ing to the formula7
Γ = q(nFA)–1
(2)
where q is the electric charge, n is the number of electrons exchanged dur-
ing the oxidation process (n = 2), F is the Faraday constant and A is the area
of the glassy carbon electrode (A = 0.071 cm2). The linear sweep voltam-
metry results were fitted according to Langmuir adsorption isotherm (Fig. 4)
which is usually expressed as
–1
–1
(Γ)–1 = (Γmax
)
+ (KceqΓmax
)
(3)
where Γmax stands for the maximum surface coverage, K is the adsorption
equilibrium constant and ceq is the equilibrium concentration of rutin.
There are two linear regions in Fig. 4. At lower concentrations of rutin (till
c(rutin) ~ 2.5 × 10–5 mol dm–3) anodic peak current is a linear function of
the rutin concentration (the adsorption of rutin oxidation products on the
electrode surface occurs). At higher concentrations of rutin (above c(rutin) ~
–5
10 (c, mol dm
–3 –1
)
FIG. 4
Langmuir adsorption isotherms of rutin in acetate buffer (Ic = 0.1 mol dm–3, pH 4.5) on the
glassy carbon electrode at room temperature (t = 25 °C) and at different scan rates. Scan rate:
20 (᭿), 50 (᭹), 100 (ꢀ) mV s–1
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Electrochemical and Antioxidant Properties of Rutin
555
2.5 × 10–5 mol dm–3), the increase of peak current slows down, which could
be explained by increase of interactions between molecules adsorbed on the
electrode surface and diffusion current6. The obtained values of maximum
surface coverage decreased with increasing scan rate from Γmax = 3.4 × 10–9
mol cm–2 at scan rate 20 mV s–1 to Γmax = 1.5 × 10–9 mol cm–2 at scan rate
100 mV s–1. Calculated adsorption equilibrium constant for rutin adsorp-
tion on a glassy carbon electrode surface was log K = 4.57 0.05.
Differential Pulse Voltammetry
Differential pulse voltammetry was used for investigation of rutin oxidation
peak current (Ip) as a function of pH (from pH 2.5 to 8.0). As is shown in
Figs 5A and 6, the highest peak current was around pH 5.5 (the same result
A
E, V vs SCE
B
E, V vs SCE
FIG. 5
(A) Differential pulse voltammograms of rutin (c = 1 × 10–5 mol dm–3) as a function of pH: 2.5
(a), 3.5 (b), 4.5 (c), 5.5 (d), 7.0 (e), 8.0 (f) at scan rate 5 mV s–1. (B) Differential pulse
voltammograms of rutin (c = 1 × 10–5 mol dm–3) in acetate buffer (Ic = 0.1 mol dm–3, pH 5.5) at
scan rate 5 mV s–1. First scan (a), second scan (b), third scan (c), forth scan (d)
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556
Medvidović-Kosanović, Šeruga, Jakobek, Novak:
was obtained by cyclic voltammetry) and it decreased in more acidic and al-
kaline media. The plot of peak potential (Ep) vs pH showed linearity (Fig. 6)
with the slope 60.6 mV, which corresponds to the mechanism involving
the same number of protons and electrons and agrees with data found in
literature5,7,9. It can be concluded that the oxidation of the 3′,4′-dihydroxy
substituent on the B-ring of rutin is a 2 e– – 2 H+ reversible process on the
glassy carbon electrode, which depends on pH.
pH
FIG. 6
Rutin oxidation peak current (Ip) and peak potential (Ep) as a function of pH
pH
FIG. 7
Dissociation diagram of rutin: undissociated form of rutin (H4A), deprotonated forms of rutin
(H3A–, H2A2–, HA3– and A4–
)
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Electrochemical and Antioxidant Properties of Rutin
557
Differential pulse voltammetry revealed a second oxidation peak of rutin
around 0.9 V. Both peaks decreased with successive scans (Fig. 5B) for all
pH studied which confirmed adsorption of oxidation products of rutin on
the glassy carbon electrode surface. The products of oxidation of rutin can
also undergo homogenous chemical reactions with water following its oxi-
dation at a glassy carbon electrode5,34
.
Dissociation diagram of rutin (Fig. 7) shows that its spontaneous de-
protonation does not occur below pH 5 which means that the neutral rutin
molecule participate in electrochemical oxidation reaction and adsorption
processes up to pH 5. At higher pH values (pH 5–8), spontaneous deproton-
ation of rutin occurs, different dissociated species of rutin are formed and
the possibility of occurrence of much more complex electrochemical and
adsorption processes exists. Dissociation constants (pKa7 = 7.35; pKa4′
=
A
E, V vs SCE
B
E, V vs SCE
FIG. 8
Square-wave voltammograms of rutin (c = 1 × 10–5 mol dm–3) in acetate buffer (Ic = 0.1
mol dm–3, pH 5.5) at scan rate 100 mV s–1. (A): first scan (a), second scan (b), third scan (c),
forth scan (d). (B): total current (It), forward current (If), backward current (Ib)
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558
Medvidović-Kosanović, Šeruga, Jakobek, Novak:
8.80, pKa3′ = 11.04 and pKa5 = 11.90) were obtained by spectrophotometry
and potentiometry35.
Square-Wave Voltammetry
Square-wave voltammograms were recorded over the same pH interval in-
vestigated by differential-pulse voltammetry. The results have confirmed
adsorption of oxidation products of rutin on the electrode surface since the
oxidation peak currents decreased with increasing scan number (Fig. 8A).
The advantage of this method compared to differential pulse and cyclic
voltammetry lies in greater speed of analysis, lower consumption of electro
active species and reduced problems with blocking of the electrode surface.
The current is sampled in positive and negative-going pulses, so the oxida-
tion and reduction peaks of electro active species can be obtained at the
same time. The reversibility of the first oxidation peak of rutin was also
confirmed since both oxidation (forward current) and reduction (backward
current) peaks appeared at the same potential, Ep = 0.33 V (Fig. 8B). A possi-
ble oxidation mechanism of rutin, which corresponds to the oxidation of
3′,4′-dihydroxy substituent on the B-ring of rutin and includes transfer of
two electrons and protons is given in Fig. 9. The mechanism involves ion-
FIG. 9
A possible mechanism of electrochemical oxidation of rutin. R = rutinose (C12O9H21
)
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Electrochemical and Antioxidant Properties of Rutin
559
ization of rutin, losing a proton to give the monoanionic species followed
by a one electron, one proton oxidation of the monoanionic species to
form a radical anion. This then undergoes a second reversible one-electron
oxidation to give dehydrorutin. The latter species is rapidly protonated and
then dehydrated to yield the final product of 3′,4′-diquinone5,7. It was
found that rutin and its oxidation products are both adsorbed on the elec-
trode surface12. The oxidation mechanism is pH dependent and the optimal
pH value for the rutin oxidation process was found to be around pH 5.5
which agrees with data found in ref.17. The second oxidation peak of rutin
found in differential pulse voltammogram, which corresponds to the oxida-
tion of 5,7-dihydroxy group on the A-ring of rutin, is an irreversible oxida-
tion process15.
TEAC Assay
The TEAC assay is an electron transfer based assay. It includes two compo-
nents in the reaction mixture, antioxidants and oxidant (also the probe)
and is based on the following electron-transfer reaction36.
probe (oxidant) + e (from antioxidant) → reduced probe + oxidized antioxidant
(4)
The probe itself is an oxidant (ABTS) that abstracts an electron from the an-
tioxidant. Antioxidant is a substance which scavenges reactive oxygen/
nitrogen species to stop radical chain reaction or it can inhibit the reactive
oxidants from being formed in the first place, causing colour changes of the
probe (from dark blue to colourless). In this study, the antioxidant capaci-
ties of rutin solutions of different concentrations, expressed as Trolox
equivalents, were determined by the classic TEAC decolourisation assay
(the procedure was taken from ref.27). It was found that TEAC values of
rutin are concentration dependant (Fig. 10), which agrees with data found
in literature37. Percent inhibition (% inhibition) of rutin was plotted as a
function of rutin concentration (data not shown) in order to determine the
EC50 value of rutin. The EC50 value is the ratio of the antioxidant concen-
tration necessary for decreasing the initial ABTS concentration by 50% to
the initial ABTS concentration. The concentration of rutin, c (in µmol dm–3),
necessary for ABTS initial concentration decrease to 50% of the initial ABTS
concentration, was calculated from linear regression equation:
% inhibition = 0.2136 c(rutin) + 8.6746 .
(5)
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560
Medvidović-Kosanović, Šeruga, Jakobek, Novak:
The determined concentration of rutin was divided with ABTS initial con-
centration (c = 1 mmol dm–3) and the obtained EC50 value of rutin was
0.23, which is similar to data found in ref.24. The results obtained in this
study could be used to explain the connection between electrochemical
properties of rutin and its biological activity.
–3
c(rutin), µmol dm
FIG. 10
The TEAC values (n = 3, SD = 0.05) of rutin measured after 1 min in different concentrations
by TEAC assay
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